Wednesday, September 7, 2016

An Alcoholic Patient with Syncope

A middle-aged male had sudden syncope. There was head injury and he was intoxicated with alcohol, but he stated "I've been way more intoxicated than this; I have no idea why I passed out."

He denied any kind of chest discomfort or dyspnea or jaw or shoulder pain or epigastric discomfort.

He was completely asymptomatic.

He had a head CT that was normal, a breath alcohol of 0.10% and had this ECG recorded:

What do you think?

As is very common, the computer did not adequately measure the QT interval. The computer did find a long QT, but greatly underestimated it.
(See this post, which also links to others: Syncope and Bradycardia)

I showed this ECG to the residents and they could not identify the abnormality. To me, it shouts in my face "long QT!" This demonstrates how important experience is to Gestalt, and how, if one does not have that experience, one must force oneself to systematically read the ECG.

You must look at every ECG, and if the QT looks long, then measure it yourself. A good rule of thumb is that if the QT is more than half the RR interval, then measure it and correct for heart rate. Importantly,at high heart rates (short RR interval), the half-the-RR rule of thumb tends to label too many QT’s as abnormal. At low heart rates (long RR interval), the rule of thumb tends to label too many as normal.

I measured the QT at 530 ms, which results in a Bazett corrected QTc of 620 ms, and that is how I interpreted the ECG at the time:

Here is the old ECG for comparison:

Normal

Since the patient is alcoholic and has a long QT, one must consider hypomagnesemia and hypokalemia. One must also consider medications, and as it turns out, the patient was on 2 psychiatric drugs which can prolong the QT.

Also, I always give any alcoholic 2 g of Mg if they are sick enough to get an IV, so we administered 2 g Mg.

He was also given IV fluids for possible dehydration.

Another ECG was recorded before the Mg was administered:

Again the QT is not correctly measured by the computerI get 500 ms, not 467. The correct QTc would then be approximately 610 ms.

There are also very large inferior T-waves, consistent with inferior hyperacute T-waves.The patient continued, however, to be asymptomatic, serial ECGs showed no change, and bedside echocardiography showed no wall motion abnormality.Therefore, I attributed these T-waves to the long QT and not to ischemia

The Mg level returned at 1.3 mEq/L (low but not terribly low, reference 1.4 mEq/L)) and K returned at 3.4 mEq/L (low but not terribly low). 2 g of Mg were administered, and then the patient was admitted, after which he received another 2 g of Mg.

The next AM, the Mg was 2.2 mEq/L and this ECG was recorded:

Near normal QTc

The patient was taken off the QT prolonging medications.

The next AM (1.5 days later) a final ECG was recorded:

The patient still has large T-waves, but the QT is normal

Assessment

Whether this patient had Torsades de Pointes (due to long QT) as the etiology of his syncope is uncertain, but such a prolonged QTc certainly puts him at high risk. The longer the QTc, the higher the risk, and that risk gets significant when the QTc is greater than 500 ms and becomes very high risk at 600 ms.

Neither the ED treating resident, nor the inpatient team, saw this long QT. The inpatient team was skeptical of my manual measurement. They were going to attribute the syncope entirely to dehydration and alcohol intoxication. I had to personally consult the cardiologists to redirect the evaluation, even though my formal interpretation stated that the QTc was 620 ms.

Physicians want to believe the computer's inaccurate measurements!

Learning Points:

1. The computer will not consistently accurately measure a very long QT.
2. Look at every ECG and visually estimate the QTc by using the half the RR interval rule of thumb.
--If it appears long, manually measure it yourself!
3. Correct for heart rate usingBazett’s formula: QTc = QT / √RR (QT divided by square root of the preceding RR interval)4. A prolonged QT can make T-waves look very large and unusual5. Check for QT prolonging medications or drugs. See these two posts.6. Check Mg and K, and give Mg to patients who drink ethanol daily.7. Even obvious very long QT may go unrecognized without systematic interpretation.

Two Questions Dr. Smith: 1. which lead do you use to measure the QTc and is there any guideline how to measure it? 2. Isn't there something like the crochetage sign in II and probably also aVF, suggesting ASD in a Patient with syncope?